PROJECT SUMMARY The KRAS oncogene is found in 25% of patient tumors across many cancer types where it plays a critical role in driving tumor growth and resistance to therapy. Its effects are so powerful that it overrides the activity of many of the new molecularly targeted signaling drugs being developed for cancer today. Despite extensive effort there is no approved treatment for mutated KRAS tumors and many patients will die of their disease. We and other groups are addressing this major unmet medical need and several new anti-KRAS drugs are currently in development. A companion biomarker is a critical requirement of the FDA Critical Path rapid approval process to get new drugs rapidly and more cheaply to patients. However, a problem for any anti- KRAS drug, and one that has been apprecated for some time but not addressed due to the absence of an effective therapy, is that only about half of cancers with mutated KRAS are KRAS addicted (that is require KRAS for their growth). Thus, although mutant KRAS provides a primary biomarker for patient selection, additional biomarker(s) are necessary to identify patients with KRAS addicted tumors. We propose to conduct studies to identify such biomarkers that can be used in the early clinical trials of anti-KRAS agents. Specifically we will study a novel small molecule inhibitor of mutant KRas cell and tumor growth we have developed, PHT- 7390, together with an inactive stereosiomer PHT-7389 as a control. Thus the hypothesis upon which the studies are based is that: ?not all mut-KRAS tumors are KRAS addicted and the discovery of a biomarker, or small panel of biomarkers, for patient selection in addition to mutant KRAS itsef, will be necessary to unlock the full potential of anti-KRAS therapy and to bring the new inhbitors rapidly and effectively to the clinic. Such biomarkers can be developed using knowledge of the biology of mutant KRAS signaling, and a small molecule inhibitor we have developed that selectively inhibits mutant KRAS, but not wild type KRAS downstream signaling and tumor growth?. Thus the objectives of the study are: 1) To use mutant KRAS addicted and non- addicted non small cell lung cancer (NSCLC) and colorectal cancer (CRC) cell lines to identify a biomarker, or limited number of functionally relevant biomarkers, predicting sensitivity to our lead mutant KRAS inhibitor, PHT-7390, compared to an an inactive stereoisomer; 2) To investigate the in vivo antitumor and drug target engagement response of the mutant KRas inhibitor PHT-7390 in addicted and non-addicted NSCLC and CRC cell line xenografts, with biomarker validation in genetically characterized patient derived tumor xenograft mice.